feat: add GHA workflow for docker test

.github/workflows/docker.yml

@@ -0,0 +1,34 @@
+name: Docker
+
+on:
+  push:
+    branches:  [ main ]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        container:
+          - 'ubuntu-20.04'
+          - 'alpine-3.17'
+        package_ruby_ver:
+          - '3.1.6'
+          - '3.2.3'
+    container:
+      image: ghcr.io/tamatebako/tebako-${{ matrix.container }}:latest
+    steps:
+    - name: Checkout sample
+      uses: actions/checkout@v4
+
+    - name: Package
+      run: tebako press -e app.rb -o sinatra.teb -r sinatra -R ${{ matrix.package_ruby_ver }}
+
+    - name: Test
+      run: ./sinatra.teb -h
+
+    - name: Look around
+      run: ls -la